True hermaphroditism, now called ovotesticular disorder of sex development (OT-DSD), is extremely rare in humans, occurring in roughly 1 in 100,000 live births. Only about 250 cases were documented in medical literature between 1956 and 2024. But the answer gets more nuanced depending on how broadly you define the question, because OT-DSD is just one condition on a wider spectrum of intersex variations that affect sex chromosomes, hormones, or anatomy.
What “Hermaphroditism” Means in Modern Medicine
The term “hermaphroditism” has largely been replaced in clinical settings by “ovotesticular disorder of sex development.” The condition is defined by the presence of both ovarian and testicular tissue in the same person. This can mean one ovary and one testis, or a single gonad containing both tissue types. OT-DSD accounts for about 3 to 10% of all disorders of sex development, and most people with it are infertile.
Incidence estimates vary widely depending on the source, ranging from as rare as 1 in 100 million to as common as 1 in 100,000 live births. The geographic variation is real: the condition appears more frequently in certain populations. In South Africa, ovotesticular DSD accounts for an estimated 4% of all sex ambiguities, with higher prevalence among Black South Africans.
Why the Numbers Depend on the Definition
If you’ve seen the claim that 1.7% of people are intersex, that figure comes from biologist Anne Fausto-Sterling and includes a wide range of conditions where sex chromosomes, hormones, or anatomy don’t fit neatly into typical male or female categories. This encompasses relatively common chromosomal variations like Klinefelter syndrome and Turner syndrome, as well as hormonal conditions like late-onset congenital adrenal hyperplasia.
Physician Leonard Sax argued that this definition was too broad. He proposed restricting “intersex” to cases where a person’s chromosomal sex is inconsistent with their physical sex, or where external anatomy can’t be clearly classified as male or female. Under that narrower definition, the prevalence drops to about 0.018%, nearly 100 times lower. Both figures are cited frequently, and which one you encounter depends on the context and the definition being used.
More Common Intersex Variations
While true ovotesticular DSD is vanishingly rare, several related conditions occur far more often. These don’t involve having both ovarian and testicular tissue, but they do affect how sex characteristics develop.
Klinefelter syndrome affects roughly 1 in 500 to 1,000 newborn males. People with this condition carry an extra X chromosome (47,XXY). It can lead to reduced testosterone production, breast tissue development, and infertility, though many people with Klinefelter syndrome go undiagnosed because the physical signs can be subtle.
Turner syndrome occurs in about 1 in 2,000 to 4,000 female live births. It results from a missing or partially missing X chromosome (45,X) and typically causes short stature, ovarian insufficiency, and certain heart or kidney differences.
Congenital adrenal hyperplasia (CAH) is a hormonal condition where the adrenal glands produce excess androgens. The classic form affects about 1 in 15,000 to 20,000 births in Western countries and can cause ambiguous genitalia in newborns with XX chromosomes. A milder, non-classic form is much more common, occurring in roughly 1 in 1,000 people and as frequently as 1 in 100 in certain ethnic groups. The milder form typically doesn’t affect genital development but can cause symptoms like excess hair growth or irregular periods later in life.
Androgen insensitivity syndrome (AIS) occurs in people with XY chromosomes whose bodies partially or fully cannot respond to testosterone. Complete AIS affects 2 to 5 per 100,000 genetically male individuals and results in a fully female external appearance despite XY chromosomes. Partial AIS is rarer, at 5 to 7 per million, and produces a range of genital appearances.
How OT-DSD Develops
In typical development, a gene called SRY on the Y chromosome triggers the formation of testes. Without it, ovaries develop instead. In ovotesticular DSD, something disrupts this process so that both tissue types form. The most common chromosomal pattern is 46,XX, found in 65 to 90% of cases.
Several genetic pathways can cause this. Sometimes the SRY gene has been accidentally transferred onto the X chromosome, triggering partial testicular development in someone with XX chromosomes. In other cases, no SRY gene is present at all. Instead, genes that promote testicular development become overactive, or genes that normally steer development toward ovarian tissue are underactive. The result is the same: both ovarian and testicular tissue develop in one person.
How These Conditions Are Identified
Some intersex conditions are apparent at birth when a newborn’s genitalia don’t clearly appear male or female. Medical teams use scoring systems that assess features like genital structure, the position of the urethral opening, and whether gonads can be felt in the groin or scrotum. Hormone testing and chromosomal analysis typically follow.
Many intersex variations, though, aren’t obvious at birth. Klinefelter syndrome is often discovered during puberty when expected development doesn’t occur, or in adulthood during fertility testing. Complete androgen insensitivity syndrome may not be identified until a teenager with female external anatomy doesn’t begin menstruating. Non-classic CAH frequently goes unrecognized until adulthood. This means the true prevalence of intersex conditions is almost certainly higher than reported numbers suggest, since mild cases often go undiagnosed entirely.
Putting the Numbers in Perspective
If you’re asking specifically about the historical concept of hermaphroditism, where one person has both ovarian and testicular tissue, it is genuinely rare. Fewer than 300 cases have been formally documented over nearly seven decades. If you’re asking more broadly how often human sex development diverges from the typical male or female pathway, the answer is considerably more common. Even using the stricter 0.018% estimate, that translates to roughly 1.4 million people worldwide. Using the broader 1.7% figure, it would be over 130 million.
The gap between those two numbers reflects a real scientific disagreement about where to draw the line between normal variation and a medically meaningful condition. What’s not in dispute is that sex development in humans is more complex than a simple binary, and that variations occur along a spectrum from extremely rare to relatively common.